Writing output to text file doesn't show input

Question

I have a C++ program that is supposed to read input from a text file, and write the output to a text file. I wanted to try an achieve this without adding any extra code, so in the command line I write

project.exe<input.txt>output.txt

This works, but in the ouput.txt file, I can't see any of the input. It just says something like:

Enter option: 
option output

I could just add std::cout<<option; after every input, but is there a way to show the input without adding any extra code?

I didn't think it mattered because I was doing it all through command prompt — Emilio Garcia, May 08 '17 at 19:58
I thought it was an issue with how I called it in command prompt, not the c++ itself — Emilio Garcia, May 08 '17 at 19:59
@Jeremy I am getting the correct output, all that's not working is that the input isn't shown in the text file. I just wasn't sure if this was the standard result from using command prompt for I/o. — Emilio Garcia, May 08 '17 at 20:04
This is a bit unclear. Unless you echo the input to stdout, it won't be in "output.txt". — molbdnilo, May 08 '17 at 20:04
@molbdnilo Ah I see, is there a way to enforce echo in the command prompt? Or should I just manually add cout's after all my inputs? — Emilio Garcia, May 08 '17 at 20:06

score 1 · Accepted Answer · answered May 08 '17 at 20:06

1

You're trying to find a way to make the Windows shell copy or clone your input stream so that, after it is consumed by your program, it is also sent to the output stream. There are some problems with that:

It was consumed by your program!
Your program has control of the output stream

I'm not saying it's impossible (on Linux, some concoction with tee may be possible), but if it's possible then it's going to be hacky and certainly unconventional.

Frankly I would stick with your own idea of just mirroring the input to the output stream, within the program itself. If someone uses your program interactively then that's going to look strange for them, but you could provide a command-line switch to toggle this functionality. It would be analogous to PuTTY's optional "local echo" feature, for example.

answered May 08 '17 at 20:06

Lightness Races in Orbit

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Thanks, I wasn't sure if it was easily doable. I had just been introduced to I/O with command prompt, so I didn't know what it was/wasn't capable of. – Emilio Garcia May 08 '17 at 20:09
Explore http://stackoverflow.com/a/7940993/560648 if you wish to cause yourself pain :) – Lightness Races in Orbit May 08 '17 at 20:09
Sorry about all the downvotes; lots of people apparently didn't understand your question, although I thought it was pretty clear. – Lightness Races in Orbit May 08 '17 at 20:10
All good. I think it's a gut reaction to downvote questions without code, and with a forum this large, it's understandable. Thanks for the link, I'll take a close look at it. – Emilio Garcia May 08 '17 at 20:17

Writing output to text file doesn't show input

1 Answers1